In recent years, battery-powered and portable personal computers show a tendency to be classified into the following two models. For example, one is a low-price model, which is configured to achieve the purpose only of operating basic software such as a browser, a mailer and a text editor. The other is a high-functional model, which is capable of enjoying an AV (audio and visual) content) with high definition and high sound quality using a large screen. Of the foregoing high-functional mode personal computers, several personal computers include a television function for watching, recording and reproducing television broadcast program data.
A personal computer including a television function is provided with a terminal for making a connection with an antenna and a television tuner unit for selecting a target channel from a plurality of channels. Further, the personal computer includes a preset function of searching (called as channel scan and channel search) and setting channels receivable in a local area where users use the personal computer. In general, the television tuner unit includes a built-in amplifier (gain control circuit) for receiving a television broadcast signal of each channel at a suitable level under the environment that users use a personal computer. Various proposals for a gain control method by the amplifier have been made so far (e.g., see Jpn. Pat. Appln. KOKAI Publication No. 2005-20302).
The foregoing Publication No. 2005-20302 discloses a television broadcast signal receiver. The television broadcast signal receiver previously stores gain setting information of an automatic gain control (AGC) amplifier. Further, the receiver determines and changes the gain of the foregoing AGC amplifier every reception channel based on reception information obtained in channel search and the gain setting information.
The foregoing television broadcast signal receiver disclosed in the Publication No. 2005-20302 determines a gain setting value (gain value) of the AGC amplifier from an input level only. For this reason, if multi-wave interference distortion occurs, it is difficult to prevent radio interference that determination of the gain value becomes complicated.
More specifically, the foregoing multi-wave interference distortion is radio interference having an influence to a reception channel when the input level of other channels is high and the number of channels is great. Therefore, if gain is set on based on the matter that the input level of the reception channel is small, the following problem arises. Specifically, if the foregoing multi-wave interference distortion exists, signals of other channels are amplified; as a result, this is a factor of generating radio interference.
Namely, a television tuner unit including a gain control function conventionally executes reception in the following manner. Specifically, the unit determines a gain control value based on reception status information obtained in channel scan, and then, sets the gain control value in the actual channel reception. For example, status information related to an input level is acquired as the reception status information. If the input level is high, gain is set off; conversely, if it is low, gain is set on. Thus, reception performance is set in accordance with the strength of an electric field.
However, distortion occurs in a reception channel radio-wave due to an influence by signals of many channels except a reception channel; as a result, radio interference is generated (i.e., the foregoing multi-wave interference distortion). Therefore, it is difficult to securely prevent the foregoing radio interference without causing an error based on the input level only because determination of the actual gain value is complicated. In view of the foregoing circumstances, it is desired to provide a method of more securely prevent radio interference such as multi-wave interference distortion in which determination of the actual gain value is complicated, without increasing time spent for channel scan (i.e., time spent for determining a gain value of each channel).